At present, in electrical packaging of printed circuit boards, the Input/Output connectors are separate devices from the printed circuit board if they are the compliant portion of the electrical connection. At times, the edge of a printed circuit board, the tongue, is a portion of the electrical connection--but it is non-compliant. That is, it does not adjust for variations in the mechanical interface. This task is the responsibility of the compliant member of the electrical connection. All electrical connectors which are designed for multiple connections and disconnections must have at least one compliant member. The compliant member, often a metal spring, is necessary to create and maintain a certain amount of interfacial pressure, or normal force, between itself and the other member to which it connects. This normal force must be maintained under varying conditions of manufacturing tolerances, assembly tolerances, expansion and contraction due to temperature changes and physical disturbances such as shock and vibration. The other member may or may not be compliant.
The compliant member is usually made of conductive material, such as a copper alloy. Therefore the compliant member generally carries the electrical current through itself. This conductive material is machined or formed into a spring and is generally overplated with protective conductive coatings such as tin or gold.
Other compliant members of an electrical connection have been made of elastomeric (rubber-like) material which, when compressed, provides the sufficient normal force for the connection. As the material is initially non-conductive, it is made conductive by selectively impregnating it with conductive material, or by overlaying a sheet of film which carries conductive traces. Another configuration or elastomeric connectors uses metal strips wrapped around the elastomeric material. The elastomeric material is not directly overplated with the metallic conductive coatings used with metal springs since such conductive coatings would crack under the compression and extension to which elastomeric connectors would be subjected.
The different types of Input/Output connectors for printed circuit boards described above require many manufacturing operations to construct the elements and to assemble the elements into their various final configurations. Additional assembly costs are then required to attach these connectors to the printed circuit board.
The concept of constructing the printed circuit board through molding and selective plating is known. Rather than starting with a planar laminate of copper clad glass epoxy, the base of a molded circuit board is produced by molding. This molding process allows the structure to have various 3-dimensional features. In order to have these 3-dimensional features on conventional planar boards, these features would have to be separately manufactured (for example, bosses and brackets) and later attached or incorporated by secondary operations.
The molded structure is further processed by selectively applying a conductive surface to it. Such processes consists of roughening the surface by mechanical means such as sandblasting or abrasion, or chemical means which attack the surface of the molded structure to increase the adhesion of the conductive layer thereto. The surface is then selectively coated with one or more conductive layers through several manufacturing operations. The Molded Circuit Board may then have components attached which are electrically interconnected, most often by soldering, but otherwise by conductive adhesives.
The present invention relates to the molding of the circuit board, together with compliant springs and a rigid protective housing for these springs. This molding process just described can be accomplished in as little as one operating step. The compliant springs are shaped like cantilever beams attached to the molded circuit board and extending therefrom. These compliant springs act as an electrical Input/Output connector for the molded circuit board.
The use of plastics as spring members requires considerable caution as they do not respond to stress in the same way as metals. A primary difference between stressed polymers and metals is a greater relaxation of stress with time with polymers. Newer engineered polymers have been tested under stress and data has been generated which can predict the amount of stress relaxation that will occur over time. The predicted values will vary with different conditions of deflection and temperature. The predictability of this stress relaxation is a basis for this invention.
An element of this invention is a non-conductive compliant member made in the molding process in the shape of a cantilever beam. The beam is then directly overplated with conductive materials like copper, nickel, tin or gold. These springs are quite small, being designed to mate with other conventional connector interfaces. It is essential that such small members be physically protected to prevent breakage due to deflection beyond the design limits. Such deflections can be in directions other than those intended or in the intended direction to an amount greater than that for which it was designed. Such deflections can be limited by a protective barrier or housing. Further, the conductive surface on the beam must be restricted from excessive flexing to prevent fracture or cracking of the thin plating on the surface. The protective restriction could be accomplished by placing a protective barrier or housing in close proximity to the spring if such a barrier could be positioned very accurately.
A further essential element of this invention is an accurately positioned rigid protective barrier or housing which is manufactured of non-conductive material positioned in close proximity to the spring. In order to very accurately position the barrier in relation to the springs, the barrier is aligned on those springs during the manufacturing process. The protective barrier or housing is produced by the same method of manufacture as the spring, by molding. A preferred method is to mold the housing of the same material, in the same mold, and at the same time as the spring. It may also be accomplished by molding in a second molding operation of a similar non-conductive material. In this instance, the housing still must be carefully and specifically positioned in reference to the springs in the second mold tool, or the other mold tool cavity in the same mold. This careful positioning is nevertheless accomplished because the housing is produced by the same process as the springs although in a different step.